This study investigates the possible prognostic role of serum metastasin messenger RNA (mRNA) in breast carcinoma as a non-invasive screening tool, and determines metastasin mRNA in the serum of breast cancer patients with high sensitivity (85%) and specificity (100%). A significant difference (P = 0.05) was observed between serum metastasin mRNA and the number of involved lymph nodes. Patients with higher expression of serum metastasin showed poor survival (six times worse) than those with lower levels. Patients negative for serum metastasin mRNA suffered recurrences, while those positive for serum metastasin mRNA suffered distant metastases. The results of this study suggest that serum metastasin mRNA represents an important survival marker in breast carcinoma.